Commercial grade 2-pyrrolidone generally contains about 1 to 2% or more by weight of certain impurities such as water, butyrolactone, 2-butyne-1,4-diol, 2-butene-1,4-diol, 1,4-butanediol, bipolar mesomer, amino acids and other unknown materials, depending upon the method by which the material was made and handled, and which do not present a problem for some end uses to which the material is applied but which render the material unsuitable for other end uses.
Several purification processes have been proposed over the years, including treatment with hydrides, hydroxides, pentoxides, acid anhydrides, various volatile solvents, and the like. However such known processes have a variety of deficiencies including a lack of efficiency resulting from a high amount of waste of the commercial grade 2-pyrrolidone. Also some of these processes are only effective with respect to 2-pyrrolidone produced according to a certain method while other proposed processes result in the production of 2-pyrrolidone which is not truly pure as evidenced by its inability to form a high viscosity homopolymer or to undergo polymerization at all and by its inability to maintain a stable clear color for more than a month or so.